1. Field of the Invention
The present invention relates to a flux composition, for a liquid flux and a solder paste, used for soldering electronic parts onto printed circuit boards.
2. Description of the Related Art
The fluxes used for soldering electronic parts and the like onto printed circuit boards include liquid types used for coating printed circuit boards by foam systems or spray systems, and paste fluxes used as solder paste in admixture with solder powder.
A conventional liquid flux is composed mainly of rosin-based resins, and is prepared by adding an activating agent such as an amine-hydrogen halide acid salt and an organic acid for increased activating power, as well as a delusterant to eliminate gloss on the solder surface after soldering, and then dissolving the mixture in a lower alcohol such as isopropyl alcohol (IPA).
A flux for solder paste is composed mainly of rosin-based resins, and is prepared by adding an activating agent, as well as a wax to give a paste, and then dissolving the mixture in a solvent with a boiling point of 200.degree. to 300.degree. C. to form a paste.
With the current total ban on freon (fluorocarbon, chlorofluorocarbon and the like), and the failure to develop a detergent with the same or better detergency as freon without environmental pollution, there is an increasing trend to leave flux residues unwashed from printed circuit boards after soldering, and hence there is a growing demand for greater reliability of flux residue remaining on printed circuit boards.
The reliability of flux residue remaining on printed circuit boards is evaluated based on insulation this paper or fee is being deposited with the resistance and migration tests under high temperature and humidity, and on moisture condensation tests, and these are almost all carried out under conditions of constant temperature or low temperature variation.
Electronic devices all undergo continuous temperature variation except for those used under constant temperature conditions and, in extreme cases such as equipment in vehicles, the temperature variation may be as great as 80.degree. C. or more. Consequently, flux residues on printed circuit boards also undergo continual temperature fluctuations, and have therefore been subject to cracking and deterioration which has resulted in impaired reliability.
It is an object of the present invention to provide a highly reliable liquid flux and solder paste flux, with which solderability is not impared, where the flux residue on printed circuit boards after soldering undergoes no cracking or deterioration even under temperature variation and which, through a damp proofing effect, prevents poor insulation and migration even under high humidity environments, as compared to conventional liquid flux and the solder paste flux commonly known as a post-flux.